An aircraft is moved by a number of turbojet engines, each housed in a nacelle that also houses a set of ancillary actuation devices linked to its operation and handling various functions when the turbojet engine is operating or stopped. These ancillary actuation devices notably comprise a mechanical system for actuating thrust reversers.
A nacelle generally has a tubular structure comprising an air inlet at the front of the turbojet engine, a mid section intended to surround a fan of the turbojet engine, a rear section intended to channel the secondary air stream from the turbojet engine and being able to house thrust reversal means, and is generally terminated by an exhaust nozzle whose output is situated downstream of the turbojet engine.
The modern nacelles are often designed to house a dual-stream turbojet engine able to generate, via blades of the rotating fan, a secondary cold air stream that is added to the primary stream of hot gases obtained from the turbine of the turbojet engine.
A nacelle generally has an outer structure, called outer fixed structure (OFS), which defines, with a concentric inner structure, called inner fixed structure (IFS), comprising a cowling surrounding the structure of the turbojet engine proper behind the fan, an annular flow channel, also called duct, designed to channel a cold air stream, called secondary, that circulates outside the turbojet engine. The primary and secondary streams are ejected from the turbojet engine through the rear of the nacelle.
Each propulsion system of the airplane thus comprises a nacelle and a turbojet engine, and is suspended from a fixed structure of the airplane, for example under a wing or on the fuselage, via a strut attached to the turbojet engine or to the nacelle.
The nacelle comprises at least one pair of cowlings, usually consisting of two half-shells of substantially semi-cylindrical form, on either side of a longitudinal vertical plane of symmetry of the nacelle, and mounted to move so as to be able to be deployed between a working position and a maintenance position in order to allow access to the turbojet engine.
The two cowlings are generally mounted to pivot about a hinge-forming longitudinal axis in the top portion (at 12 o'clock) of the reverser. The cowlings are held in the closed position by means of locks positioned along a junction line situated in the bottom portion (at 6 o'clock).
The nacelle can include, for example, a pair of fan cowlings, designed to cover the fan portion of the turbojet engine, and a pair of reverser cowlings, comprising a thrust reverser and covering the rear portion of the turbojet engine.
Each cowling is opened using at least one actuator, for example a cylinder, and is held open using at least one connecting rod, the actuator and the connecting rod each having a first end generally fixed to the turbojet engine and a second end fixed to the cowling.
As is known, the actuators can be produced in the form of hydraulic actuators.
It is also known to use electromechanical actuators to displace certain portions of the nacelle, such as the thrust reverser cowlings, as described in the document EP0843089. These actuators generally include an electromechanical brake for holding in the deployed position. This brake can have a rest position, the electrical power supply being disconnected, in unlocked mode or in locked mode, depending on the applications.
The document U.S. Pat. No. 6,622,963 describes, for its part, a control system wherein different means of controlling the movements of the cowling can be linked to one and the same source through the intermediary of a switch. Such a system does not make it possible on its own to be able to control several actuator motors using different power supply voltages.
Indeed, in their electromechanical version, the actuators of fan and thrust reverser cowlings can use distinct power sources. Connecting these actuators to the aircraft power supply network poses the following problems.
The presence of several actuators, that do not necessarily use the same power supply voltage, entails producing an electronic unit that handles a number of conversions of the power supply voltage to each of the power supply voltages of the actuators.
Furthermore, the presence of the actuators generates conducted and radiated disturbances on the network that necessitate filtering of the signal in this electronic unit.
This electronic unit is powered up when the airplane is on the ground and the engine is stopped. Now, its confined environment between the cowlings of the nacelle and the engine subjects it to thermal stresses after the engine has been stopped: it is subject to the solar radiation on the cowlings and to the radiation from the engine that is still hot after the flight. Keeping the unit powered up, with the actuators at rest and the cowlings closed, also brings about a release of heat specific to the unit which can affect the thermal dimensioning of the latter.